1. Field of the Invention
The present invention relates generally to an apparatus for removing particulate matter from a gas stream, and more particularly, to an apparatus for adding electrostatically charged sorbent particles to a gas stream containing particulate matter and directing the gas stream through moving bed granular media filters for removing the entrained particulate matter and sorbent particles from the gas stream.
2. Description of the Prior Art
Air pollution control methods for the removal of fine particulate matter, particularly submicron particles, are not particularly suitable when employed in sizes required for use in large volume processes. The state-of-the-art particulate removal systems experience substantial difficulties attempting to meet strict requirements and regulations imposed by governmental agencies for the removal of such particulate matter. Further, the removal of noxious gases without the accompanying generation of non-disposable wastes also presents significant problems to present industrial gas cleaning systems.
Present fine particulate gas collection systems exhibit poor efficiencies on submicron particle size particulates that must be removed from a gas stream. In those gas streams containing noxious gases such as sulfur dioxide, present systems impose the requirement of a wet or slurry system to remove the noxious gas which therefore exposes the equipment to scaling potential; further, the frequent generation of acid mists when using a wet system creates a difficult collection problem and subjects the equipment to corrosion. The use of fabric filter collectors to capture the particulates presents a fire danger and results in the requirement that temperatures be reduced which may in turn cause temperatures approaching acid dew points. In addition to the approach to acid dew points resulting from the reduced temperature, recoverable heat is lost thereby imposing an additional inefficiency in the process. Such prior art systems also represent extremely high capital costs together with high operation and maintenance costs.
The removal of particulate matter from a gas stream using electrostatic techniques is well known. The use of typical electrostatic techniques combined with systems for the removal of sulfur dioxide are subject to the difficulties described above. Some suggestions have been made regarding the use of granular bed filters for the removal of particulates. See, for example, a discussion of dust deposition published in the Journal of the Air Pollution Control Association, volume 28, no. 4, page 354 et. seq., "Dust Deposition and Granular Bed Filters: Theories and Experiments" by G. I. Tardos et al. Suggestion has also been made that such a granular bed be electrified and the gas particles be electrostatically charged such that when the gas containing the particulate matter is passed through the electrified bed the particulate matter adheres thereto. Such electrified bed equipment is discussed in a brochure entitled, Particulate Control Systems, published by Electrostatics, Inc. of Woburn, Ma. Regardless of the prior art system that is used, a balance is struck between the thoroughness of collection and the difficulties (and therefore costs) created by the collection system.
In the above mentioned copending application Ser. No. 966,096, which is hereby incorporated by reference, a novel method of removing particulate matter from a gas stream is disclosed; the disclosed method overcomes substantially all of the problems associated with prior art particulate removal systems mentioned above. The above mentioned copending patent application discloses that conventional fluidized-bed electrostatic power coating guns may be used to inject charged sorbent particles into the dirty gas stream for inducing electrostatic charges on the particulate matter entrained by the gas stream. However, in operating plants of the type which emit gas streams containing relatively large amounts of particulate matter (e.g., coke ovens, sinter plants, steel-making furnaces), application of the particulate removal method disclosed by the above mentioned copending patent application would require that sorbent material be injected into the gas stream at the rate of hundreds of pounds per minute. Conventional powder coating guns lack the capacity to inject sorbent material into the gas stream at such a rate.
Accordingly, it is an object of the present invention to provide an apparatus for applying the particulate removal method disclosed by the above mentioned copending patent application to large operating systems such as coke ovens, sinter plants, and steel-making furnaces.
An apparatus for applying the particulate removal method disclosed by the above mentioned copending patent application would typically include an inlet plenum for mixing the injected sorbent material with the gas stream and for directing the gas stream to the granular media filter. If the particulate removal apparatus is used to filter the gas stream emitted from a relatively large operating plant, such as a coke oven, sinter plant, or steel-making furnace, then large quantities of the particulate matter entrained by the gas stream will likely be deposited within the inlet plenum before reaching the granular media filter, thereby restricting the flow of the gas stream and reducing the effectiveness of the particulate removal apparatus.
Accordingly, it is another object of the present invention to provide an apparatus for applying the particulate removal method disclosed by the above mentioned copending patent application while preventing significant amounts of particulate matter from collecting within the inlet plenum.
In addition, an apparatus for applying the particulate removal method disclosed by the above mentioned copending patent application to filter the gas stream of a relatively large operating plant, such as a coke oven, sinter plant or steel-making furnace, would likely include a plurality of granular media filters, as opposed to a singular granular media filter, due to practical limitations in the sizes of materials used to construct such filters. If multiple moving bed granular filters are employed to filter the particulate matter from the gas stream, then granular media must be distributed to each of the filters. Ordinarily, a separate media supply system would be provided for each such filter. However, the addition of a separate media supply system for each filter cell greatly increases the cost of a particulate removal system as the capacity of the system, and correspondingly the number of filters, is increased.
Therefore, it is a further object of the present invention to provide an apparatus for applying the particulate removal method disclosed by the above mentioned copending patent application which uses a single media supply system to supply granular media to multiple granular media filters.